A special effect system for achieving a special effect with television signals was proposed, for example in U.S. Pat. No. 4,965,844, in which a television signal is digital-signal-processed to display the image, as if the input image has been pasted (hereinafter referred to as "mapped") on a three-dimensional curved surface (for instance, on a cylinder or a wine glass, etc., referred to as a "shape").
In a method of this type of image transform, at first, the input image is divided into blocks having a predetermined size, and the image data of each block are stored progressively in predetermined addresses of a memory according to predetermined write address data.
At the same time, a predetermined calculation is executed with respect to the addresses of stored input image data prior to transform based on the transform-input-data inputted by an operator using separate input means, thus obtaining the read addresses of the input image data stored in the memory.
The read address is calculated so that an output image which looks as if the inputted image has been mapped onto a predetermined shape can be obtained when the output image is assembled with raster scan, and in accordance with this read address, the image data of a block stored in a predetermined address in the memory is read out. Thus, a two-dimensional plane output image, which looks as if the input picture has been mapped onto a predetermined shape, can be outputted.
In the image transform, by enabling the formation of a shape such as a ripple spreading over a water surface, it would be more convenient to map various input images.
At this time, if the shape on which the image is mapped can be formed such that the amplitude of the ripple or wave becomes smaller as it goes farther from the point at which the ripple originates, a more realistic looking image can be synthesized.